In the cementing of a completed well, it is desirable to pump an unset slurry into the annular space on the exterior of casing to protect the well. It is desirable to bond the casing in place to assure that there is no fluid flow in the annular space on the exterior of the casing. This cement prevents contamination of salt water into fresh water artesian strata penetrated by the well. Such communication up and down the well is highly undesirable. For this reason, the well is typically cemented to assure that such leakage does not occur. During the process of cementing, a large supply of cement in dry form is set aside. The dry cement is delivered to a mixer, the mixer being provided with a flow of water. The dry cement is mixed with water and pumped to the well.
The density of the cement must be adjusted from time to time to assure that the cement has the desired properties. When the cement is mixed, it is mixed to a desired density. The density is preferably made somewhat high in this procedure whereby density is subsequently diluted by additional water added to the slurry. The mixing of cement with water to obtain a first density typically exceeds the required slurry density to enable the easier second step to provide dilution thereafter. Dilution is more readily handled by means of a supplemental water liner which adds water. This line is connected through a valve and turbine flow meter to monitor and control the rate of flow. The control system of this disclosure is preferably connected to the flow meter whereby the flow of water can be increased or decreased, perhaps decreasing even to zero, to modify the slurry density to the desired value.
A turbine flow meter in the slurry line cannot be readily maintained. The slurry is abrasive, tending to damage and destroy measuring devices placed in the flow lines conducting slurry to the well. In view of the slurry flow rate, it is difficult to accurately get the needed measurement from the flow line. It is also difficult to measure the dry cement flow rate. Yet, the dry cement flow rate and slurry flow rate are both important and can be obtained by the present apparatus.
The apparatus of this disclosure sets forth a control system collaborating with flow meters for the water and a meter which measures the density of the slurry. A specified density can be targeted; this control system aids and assists in adjusting the density to the desired value.